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NEET Chemistry Metallurgy / धातुकर्म Question Bank Self Evaluation Test - General Principals and Process of Isolation of Elements

  • question_answer
    One of the processes used for concentration of ores is Froth floatation process. This process is generally used for concentration of sulphide ores. Sometimes in this process we add NaCN as a depressant. NaCN is generally added in case of ZnS and PbS minerals. What is the purpose of addition of NaCN during the process of Froth floatation?

    A) NaCN causes reduction by precipitation

    B) A soluble complex is formed by reaction between NaCN and ZnS while PbS forms froth

    C) A soluble complex is formed by reaction between NaCN and PbS while ZnS forms froth

    D) A precipitate of \[Pb{{(CN)}_{2}}\] is produced while ZnS remain unaffected.

    Correct Answer: B

    Solution :

    [b] \[NaCN+ZnS\xrightarrow{{}}\underset{Soluble\text{ }complex}{\mathop{N{{a}_{2}}\left[ Zn{{\left( CN \right)}_{4}} \right]}}\,\] A layer of this zinc complex is formed on the surface of ZnS and due to this ZnS is prevented from the froth formation while PbS form froth. (i.e, NaCN is added as depressant for ZnS)


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